The present invention relates to a wound dressing, especially to a nano-silver wound dressing.
Silver has been used as a bactericidal agent for a long time. Silver works as an antimicrobial through a number of pathways. It acts on the cell wall so as to inhibit cell wall replication. Silver can also inactivate cellular respiratory chain and block energy supply of cells, or directly act on nucleic acids such as RNA and DNA. With those functions, the bacterium is either inhibited from replication or is killed. Because silver affects so many sites within cells, it has antimicrobial activity against multiple micro-organisms including bacteria, virus and fungi. In the past, most of silver being used is silver salt such as silver nitrate. However, it's highly toxic so that they are not as practical as chemical bactericides or antibiotics. However, due to antibiotic abuse, a broad spectrum of bacteria has become resistant to antibiotics. As to bactericidal agents for external use, they may have toxicity for human tissue cells. Moreover, they can only fight against certain bacteria; it is not effective for over 500 species of bacteria.
In recent years, nano-silver technology has been a research trend. Nanocrystalline silver results in a very large specific surface area for the release of ionic silver. Even only a small amount of silver provides a bactericidal action. Moreover, the silver ion is released into the wound for long-lasting bactericidal effect in a controlled fashion. It's economic and effective. Furthermore, the development of antimicrobial resistance to silver would be extremely rare and the silver further enhances wound healing. Therefore, the silver has been hot since the new century. For example, American medical products such as Acticoat produced by Smith & Nephew Co. and Silverlon produced by Argentum Medical, LLC are silver-coated wound dressings. They invest a lot of money and labor on various kind of tests such as tests of skin irritation, skin toxicity, cytotoxicity, hemolysis, systemic toxicity, and carcinogenicity, damages to liver, kidney and blood, antimicrobial activity against various bacteria, fungi and virus, wound healing test, and so on. The wound dressings have been approved by the FDA (food and drug administration). Besides the above two dressings for wounds and burns Silvasorb of Medline Co., Aquacel of Convatec Co., Arglaes of Medline Co., and Contreet of Coloplast Co. are all non-woven dressings with nanocrystalline silver. The release of the silver ion is in a controlled fashion and with long-lasting efficacy. The dressing can be left in place for seven days without replacement.
As to wound dressing made from activated carbon fiber with silver, it is quite rare as only one product-Actisorb of American Johnson & Johnson company is available. It consists principally of activated carbon impregnated with metallic silver produced by heating a specially treated fine viscose fabric under carefully controlled conditions, but it has no hemostatic function. Refer to GB2206495A, this is a military hemostatic and antitoxic dressing made by activated charcoal cloth fabric and absorbent gauze. However, due to capillary action of the absorbent cotton, it may have problems of blood leaking with poor blood staunching function, it is not antibacterial dressing. Only a disinfected, antitoxic dressing disclosed in Taiwanese Utility patent No. 114129 has all three features disinfection, antitoxicity and blood staunching. In this patent, the absorbent cotton is replaced by Superabsorbent Polymer (SAP) whose volume is enlarged after absorbing blood so as to make the bandage have adverse pressure, pressing on the wound site for better blood staunching effect. Moreover, the activated carbon fiber with silver treated by a heating process is used to achieve antitoxic and disinfected effects.
However, the carbon fiber with silver pretreated by a heating process can only be produced by large-scale factory such as charcoal cloth company in United Kingdom and the price is quite expensive-about $ NT150 dollars per 10 square centimeters with the amount of silver 3 weight percent (wt. %).